In recent years, many fabrics have been developed which the various manufacturers claim are moisture-vapor permeable. These materials are commonly described as breathable fabrics, and they normally incorporate a continuous polymer film. The film may be in the form of a thin coated layer applied directly to a fabric, or as a pre-cast film subsequently bonded to the fabric thermally or with an adhesive layer. The direct coatings may comprise one complete layer or more usually a series of different layers, for example, a base coat or tie coat directly attached to the fabric, one or more intermediate coats, and an outermost or top coat. The direct coating may therefore have the same polymer composition throughout, but more usually comprises a series of different polymer compositions applied by successive coating operations, in particular, the base coat and top coat usually have a substantially different polymer composition.
The complete coatings, separate coated layers, pre-cast films and adhesives may be formed from microporous polymers or hydrophilic polymers, or various combinations thereof may be used in the manufacture of breathable materials. A useful reference book for this technology including descriptions of manufacturing techniques and machinery is “New Materials Permeable to Water Vapour”, Dr. Harro Träubel, Springer-Verlag (Berlin), 1999.
The major use of breathable materials is in the high-performance apparel area, although these materials are also used in footwear and industrial clothing as well as some other non-apparel applications such as military and first responders. The moisture-vapor permeability of the polymer membrane is sufficient to allow sensible and insensible perspiration to diffuse away from the body.
Styrenic block copolymers are well known in the art. Generally, styrenic block copolymers (“SBC”) can comprise internal polymer blocks and terminal end polymer blocks comprising chemically different monomer types thereby providing particular desirable properties. As an example, in a more common form, SBC's may have internal blocks of conjugated diene and external blocks having aromatic alkenyl arenes. The interaction of the differing properties of the polymer blocks allow for different polymer characteristics to be obtained. For example, the elastomer properties of internal conjugated diene blocks along with the “harder” aromatic alkenyl arenes external blocks together form polymers which are useful for an enormous variety of applications. Such SBC's can be prepared through sequential polymerization and/or through coupling reactions.
It is known also that SBC can be functionalized in order to further modify their characteristics. For example, SBC can be modified by introducing functional groups such as carboxylic acids, esters or amides, phosphonate groups or sulfonate groups to the backbone of the polymer. Methods for incorporating functional groups into polymers containing unsaturation are taught, for example, in U.S. Pat. Nos. 3,135,716, 3,150,209, and 4,409,357. Alternative procedures in which functional groups are incorporated into hydrogenated SBC are taught, for example, in U.S. Pat. Nos. 4,578,429, and 4,970,265.
One of the first SBC functionalized by addition of sulfonic acid or sulfonate ester functional groups to the polymer backbone is disclosed, for example, in U.S. Pat. No. 3,577,357 to Winkler. The resulting block copolymer was characterized as having the general configuration A-B-(B-A)1-5, wherein each A is a non-elastomeric sulfonated monovinyl arene polymer block and each B is a substantially saturated elastomeric alpha-olefin polymer block, said block copolymer being sulfonated to an extent sufficient to provide at least 1% by weight of sulfur in the total polymer and up to one sulfonated constituent for each monovinyl arene unit. The sulfonated polymers could be used as such, or could be used in the form of their acid, alkali metal salt, ammonium salt or amine salt. According to Winkler, a polystyrene-hydrogenated polyisoprene-polystyrene triblock copolymer was treated with a sulfonating agent comprising sulfur trioxide/triethyl phosphate in 1,2-dichloroethane. The sulfonated block copolymers were described as having water absorption characteristics that might be useful in water purification membranes and the like, but were later found not to be castable into films (U.S. Pat. No. 5,468,574).
More recently, U.S. Pat. No. 7,737,224 to Willis et al., disclosed the preparation of sulfonated polymer and illustrated a sulfonated block copolymer that is solid in water comprising at least two polymer end blocks and at least one saturated polymer interior block wherein each end block is a polymer block resistant to sulfonation and at least one interior block is a saturated polymer block susceptible to sulfonation, and wherein at least one interior blocks is sulfonated to the extent of 10 to 100 mol percent of the sulfonation susceptible monomer in the block. The sulfonated block copolymers are described as being able to transport high amounts of moisture-vapor while at the same time having good dimensional stability and strength in the presence of water, and as being valuable materials for end use applications which call for a combination of good wet strength, good water and proton transport characteristics, good methanol resistance, easy film or membrane formation, barrier properties, control of flexibility and elasticity, adjustable hardness, and thermal/oxidative stability.
Additionally, WO 2008/089332 to Dado et al., discloses a process for preparing sulfonated block copolymers illustrating, e.g., the sulfonation of a precursor block polymer having at least one end block A and at least one interior block B wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation wherein said A and B blocks are substantially free of olefinic unsaturation. The precursor block polymer was reacted with an acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent. According to Dado et al., the process results in a reaction product which comprised micelles of sulfonated polymer and/or other polymer aggregates of definable size and distribution.